POS0012 THE EXPANSION OF CD4CD8 DOUBLE-POSITIVE T CELLS OF CD4 ORIGIN IS SPECIFIC FOR RHEUMATOID ARTHRITIS AND LINKED TO DISEASE ACTIVITY
Authors: P. Nguyen, F. Beck, M. Melzer, A. M. Glimm, M. Krasselt, O. Seifert, M. Pierer, K. Rothe, U. Wagner
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> CD4CD8 double-positive (DP) T cells are expanded in rheumatoid arthritis (RA) and associated with erosive disease [1]. The majority of DP T cells in the periphery have an effector phenotype and were reported to originate from either CD4 or CD8 single-positive (SP) T cells [2]. DP T cells of CD4 origin express a CD8αα homodimer, corresponding to a CD4+CD8<sup>low</sup> fluorescence pattern in flow cytometry, while DP T cells of CD8 origin express a CD8αβ heterodimer, which results in a CD4+CD8<sup>high</sup> pattern. Reports on the presence of polyfunctional CD4+CD8<sup>low</sup> T cells in RA patients and individuals at risk of RA (3) suggest DP T cells of CD4 origin to be relevant for RA pathogenesis. <h3>Objectives</h3> This study aims to confirm and characterize the role of DP T cells of CD4 origin, or CD4+CD8<sup>low</sup> T cells, in the context of RA. <h3>Methods</h3> DP T cells and their subpopulations were measured by flow cytometry in the peripheral blood of 53 newly diagnosed RA patients and compared to a cohort of patients with psoriatic arthritis (PsA) (n=52), as well as age-matched healthy donors (n=50). The CMV infection status of all subjects was assessed by a CMV IgG and IgM ELISA. In an independent cohort of 70 RA patients, the surface markers LIR1 and PD1 were measured on all T cells using flow cytometry. Lastly, a prospective study followed the changes in CD4+CD8<sup>low</sup> T cell frequency in patients with early RA treated with MTX or Abatacept. <h3>Results</h3> Only DP T cells of CD4 origin (CD4+CD8<sup>low</sup>) are significantly expanded in RA (figure 1A), while the frequency of DP T cells of CD8 origin (CD4+CD8<sup>high</sup>) is similar to patients with PsA and healthy controls. The expansion of CD4+CD8<sup>low</sup> T cells is associated with latent CMV infection in all three cohorts. However, CMV+ RA patients have significantly more DP T cells of CD4 origin than CMV+ healthy controls (figure 1B), indicating that CMV positivity is not the only driver of DP T cell expansion. DP T cells of CD4 origin express the senescence marker LIR1 and the exhaustion marker PD1 more often than their CD4 SP counterparts (figure 1C). In RA, CD4+CD8<sup>low</sup> T cells correlate with DAS28-CRP (r=0.35, p=0.01), indicating a link with disease activity. The frequency of CD4+CD8<sup>low</sup> T cells were measured in early RA patients before treatment (visit 1, V1), after one month (visit 2, V2) and three months (visit 3, V3) of treatment. Clinically efficacious treatment with abatacept was found to significantly reduce the frequency of CD4+CD8<sup>low</sup> T cells after three months (mean change -0.09%, p=0.02), while methotrexate treatment did not (mean change -0.03%, p=0.83, figure 1D). <h3>Conclusion</h3> DP T cells of CD4 origin (CD4+CD8<sup>low</sup> T cells) are frequently expanded in the peripheral blood of RA patients, but not in PsA patients or age-matched healthy individuals. DP T cells of CD8 origin are not expanded in RA or PsA compared to healthy controls. The association of CD4+CD8<sup>low</sup> DP T cells with CMV seropositivity, as well as the increased LIR1 and PD1 expression, suggest they belong to a chronically stimulated, antigen-experienced cell population. Importantly, these cells are associated with disease activity in RA and show a significant reduction in the peripheral blood after treatment with a T cell-targeting agent. This confirms their role in RA pathogenesis and suggests their potential as a therapeutic target or biomarker for response. <h3>References</h3> [1]Nguyen P, Melzer M, Beck F, Krasselt M, Seifert O, Pierer M, et al. Expansion of CD4+CD8+ double-positive T cells in rheumatoid arthritis patients is associated with erosive disease. Rheumatology. 2022 Mar 1;61(3):1282–7. [2]Overgaard NH, Jung JW, Steptoe RJ, Wells JW. CD4+/CD8+ double-positive T cells: more than just a developmental stage? Journal of Leukocyte Biology. 2015 Jan;97(1):31–8. [3]Floudas A, Neto N, Orr C, Canavan M, Gallagher P, Hurson C, et al. Loss of balance between protective and pro-inflammatory synovial tissue T-cell polyfunctionality predates clinical onset of rheumatoid arthritis. Annals of the Rheumatic Diseases. 2022 Feb 1;81(2):193–205. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.